It has long been known that the electromagnetic elements of rotating electrical machinery such as electrical generators and motors incur energy losses during their operation and that the losses are evident by the heat generated within the machine components. It has also been long known to include various mechanisms for removing such heat in order to maintain a normal and efficient energy transformation with such dynamoelectric devices.
It is conventional, for instance, to cool the rotor and stator elements of such devices with air or some other gas flowing through somewhat elaborate cooling ducts incorporated into the rotating machinery elements.
Still other electromagnetic rotating devices have included highly conductive laminations within the core material for the purpose of providing a path of heat conductance to an outer region where the heat may be removed, for example, through the use of forced air flowing over the outer surface of the core material. Other prior art approaches have also been utilized. For example, the concept of using liquid in copper tubing in order to cool electrical conductors is well known and has been employed for many years in large commercial generators. Such tubing, for instance, has been used to form the liquid cooled armature bars and circuit rings of such generators. Although such an approach to cooling presents problems related to maintaining appropriate supplies of dielectric coolant liquids, such an approach offers superior results since the liquid is in direct contact with the copper conductors, thus offering direct cooling whereby the heat passes from the copper directly into the coolant liquid. As will be appreciated, such direct cooling offers a significant advantage over other cooling systems. Such an advantage is useful, particularly in those instances where high power density electrical machinery is desired, since such machinery must be both physically compact and yet have maximum power output.
Although the above noted background pertains primarily to the general design of rotors and stators, such cooling approaches are also applicable to the design of circuit ring-bus bar assemblies, for example, which function to collect electrical current from a number of parallel circuits in an armature winding and conduct that current to a single machine terminal. In dynamoelectric machines there are typically two circuit rings and bus bars for each phase such that a three-phase machine would have six such assemblies, and a six-phase machine would have twelve and so forth. A set of such rings is normally stacked axially at one or both ends of the machine where the circuit leads exit from the armature winding.
In the design of such assemblies it is well known that electrical connections between the rings, leads and bus have the highest reliability when it is possible to braze or solder the conductors. Bolted joints are used where the joint size is sufficiently great as to eliminate brazing or render such techniques impractical. Moreover, a bolted joint is preferred only when it is necessary to frequently disassemble the joint or, as noted above, when other joining techniques are not practical.
When using such bolted joints, the transfer of electrical current relies on the mechanical contact at the interface of a lead connector, for example, and the circuit ring. Efficient and safe current transfer is insured only so long as good mechanical contact is maintained by way of the pressure exerted by the bolts.
In a typical circuit ring-bus bar assembly, current enters the ring at several locations about its periphery by way of leads and connectors bolted to the ring. Thereafter, the current travels around the circuit ring to the bus bar, which is also typically bolted to the ring, but which is significantly larger than any one of the circuit leads. Such ring assemblies are typically attached to a stainless steel shroud which provides mechanical support for the rings by way of electrical insulation which is placed between the rings and the shroud. Although such shrouds may be air or water cooled to provide cooling by thermal conduction from the copper circuit ring such an approach is inferior to the aforementioned direct contact of a cooling liquid with the copper since in the former arrangement the heat must pass through layers of insulation and steel before reaching the coolant. By comparison with direct cooling the heat would pass from the copper directly into the water.
As an additional problem in the design of circuit ring-bus bar assemblies, it is difficult, if not impossible, to braze the circuit lead clips to the circuit ring without damaging insulation between rings. Such damage occurs since the insulation in a stack of rings cannot be moved away from the joint when the brazed connection is being made.
We have discovered that fabricating the rings from hollow copper tubing preferably of a rectangular cross section with the tubing formed into a substantially complete circle, but with the two end portions of the copper tubing formed into an elongated parallel arrangement, offers several advantages with respect to the known prior art.
For example, by applying liquid coolant, such as water, to the construction of the circuit ring conductor such that it enters one parallel end of the tubing and travels circumferentially through the ring to exit at the other parallel end, produces superior cooling and allows the ring size to be reduced, thus allowing brazed electrical connections rather than bolted joints.
A further advantage of this invention is that of fabricating circuit ring-bus bar assemblies in such a manner as to combine the functions of the circuit ring and bus bars into a single assembly, thus eliminating a hydraulic-electrical joint.
A further object and advantage of the invention is that of maintaining a lower average temperature in the conductor, thus improving the reliability of the assembly.
Still further the invention disclosed herein employs direct internal liquid cooling of the circuit rings, thus reducing their size and providing more space from the insulation between adjacent circuit rings to the joint at the circuit lead connection. Such additional space permits the circuit lead connector to be brazed rather than bolted to the circuit ring and additionally makes it possible to reduce the height of the insulation between circuit rings, thus spacing the insulation from the joint and allowing brazing to occur.
Furthermore, in accordance with the disclosed structure and method it is possible to circulate cooling fluid such as air or water through the hollow circuit ring while brazing the circuit lead connectors in order to further assure prevention of damage to the insulation.
This invention provides high power density machinery with enhanced thermal performance. Such machinery may be used in a variety of applications, such as high frequency ship service generators, aerospace generators, drive motors and the like. Still other applications will occur to those skilled in the pertinent art.
These, as well as other objects and advantages of the invention, will be more completely understood and appreciated by careful study of the following description of presently preferred exemplary embodiments taken in conjunction with the accompanying drawings of which: